The present invention relates to a configuration magnet and a method for producing the same, and more particularly relates an improvement in the construction and method of producing a configuration magnet most advantageously used for electroacoustic converters such as loud-speakers and telephone receivers.
In construction of an electro-acoustic converter such as a loud-speaker or a telephone receiver, a conductive or permiable mobile element such as a voice coil has to be surrounded by a magnetic circuit.
Such a magnetic circuit is in general formed by a cylindrical permanent magnet properly bonded to a soft steel magnetic conductor, such as a yoke or a pole, which is shaped into a magnetic circuit. The soft steel used for this purpose, however, is not a good magnetic conductor. In addition, in terms of magnetic operation, the bond layer between the permanent magnet and the magnetic conductor acts as a mere open space and hampers the operation of the permanent magnet. In order to avoid such problems, it is ideal to form most parts of the magnetic circuit by a permanent magnet which has magnetic anisotropy substantially parallel to the extension of the circuit.
Several types of configuration magnets have already been proposed in order to meet this requirement for excellent magnetic circuits. In one example, application of radial magnetization is employed in a process for forming a configuration magnet by compaction and sintering of ferrite magnet powder. The configuration magnet produced by this process, however, does not possess satisfactory radial magnetic anisotropy. In another example, a configuration magnet is obtained by cutting a block of magnet, but this process does not develop radial magnetic anisotropy over the entire plate surface of the product.
As a result of intense study on production of a configuration magnet with ideal radial magnetic anisotropy, the inventors of the present invention realized that the above-described requirement can well be met by making use of high plastic workability of Fe-Cr-Co alloy in production of such a configuration magnet.
It is already known to the public by disclosure in, for example, Japanese Patent Publication No. Sho. 57-10166 to produce a high quality magnet with mono-directional magnetic anisotropy from Fe-Cr-Co alloy by the combination of solution treatment, magnetization, cold working or warm working at a temperature 100.degree. C. lower than the curie point, and age-hardening.
The inventors of the present invention have further advanced from this conventional proposal for use of Fe-Cr-Co alloy and tried to make use of the very fact that Fe-Cr-Co alloys have high plastic workability corresponding to that of pure iron before application of age-hardening.